A recent development in the improvement of resolution and of contrast on optical display screens has involved the use of a large number of light-absorbing fibers that are embedded in a layer of the screen and that are aligned in a direction which is parallel to the line-of-sight of an operator of the device. The absorption of oblique light rays of both internal and external origin has served to reduce the ordinary diffusion and halation, as well as significant amounts of reflection of ambient light from various layers of the screen. This development is especially effective when the screen is directly viewed by the operator, particularly at a distance such that the angle of view to all parts of the screen is essentially the same. Such a display screen is disclosed in commonly-assigned, co-pending patent application Ser. No. 500,623.
However, in some applications, it is desirable to pass the optical image from the face of a CRT into a system that includes one or more lenses in which the image may be focused, magnified, transmitted, projected, or otherwise manipulated and utilized. Under a certain class of such circumstances, the first or collecting lens of the lens system (which is co-axial with the fibers at the center of the screen) may receive non-uniform intensity of light from various parts of the display screen. More specifically, the intensity may diminish as a direct function of the lateral distance from the center of the screen. This is because, in screens of the class described, a given point-source of light in the phosphor layer produces, in effect, only a relatively narrow "cone" of light in response to the fibers in the screen. Clearly, such a screen passes undiminished light intensity to the collecting lens most effectively when the axis of each such "cone" passes near the center of the collecting lens. Thus, as much as possible of the emitted light falls on the effective collecting area, especially on the minimally-distorting central part of the lens. In the screens thus far described, a significant amount of light from peripheral areas does not fall in this manner on the collecting lens. This difficulty with the prior development has been obviated in a novel manner by the present invention.
It is therefore an outstanding object of the present invention to provide an image enhancing optical display screen which can be used in conjunction with a lens system to transfer a uniformly intense image.
Another object of this invention is the provision of an image-enhancing optical display screen which presents a uniform intensity of image with respect to a given viewing point.
Another object of the invention is the provision of a focusable optical display screen which is simple and integral in construction, which is inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.